Fullerene derivative blends, methods of making and uses thereof

ABSTRACT

Fullerene derivative blends are described herein. The blends are useful in electronic applications such as, e.g., organic photovoltaic devices.

This patent application is a continuation of U.S. patent applicationSer. No. 17/167,792, filed on Feb. 4, 2021, now U.S. Pat. No.11,296,278, which is a divisional of U.S. patent application Ser. No.16/717,711, now U.S. Pat. No. 10,950,795, filed Dec. 17, 2019, whichclaims the benefit of the earlier filing date of U.S. Provisional PatentApplication No. 62/780,569, filed on Dec. 17, 2018, the contents ofwhich are incorporated by reference herein in its entirety.

INCORPORATION BY REFERENCE

All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Thepatent and scientific literature referred to herein establishesknowledge that is available to those skilled in the art. The issuedpatents, applications, and other publications that are cited herein arehereby incorporated by reference to the same extent as if each wasspecifically and individually indicated to be incorporated by reference.In the case of inconsistencies, the present disclosure will prevail.

FIELD OF THE INVENTION

The instant application relates generally to materials. Moreparticularly, the instant application relates to fullerene blends andphotovoltaic devices comprising fullerene blends.

BACKGROUND

Organic photovoltaic devices (OPVs) based on liquid processed bulkheterojunction have significant potential to be used for an increasingnumber of applications where low weight, flexibility or the capabilityto generate power at a limited level of irradiation (e.g., for indoorenergy harvesting) are required. However, the wide-spread implementationprefers a sufficiently high-power conversion efficiency (PCE) thatremains largely stable during the lifetime of the device. Over the lastyears, the development of new classes of low-band-gap polymers allowinga more efficient absorption of the solar light resulting in theefficient formation of excitons followed by charge transport to theelectrodes has made significant progress. However, while the initial PCEof devices using such polymers as electron-donor materials has increasedsignificantly in many cases, stability, as assessed, for instance, bymeans of light soaking experiments, was often disappointing.

SUMMARY

In one aspect of the invention, a composition is provided comprising afirst fullerene derivative and a second fullerene derivative; whereinthe first and second fullerene derivative are of different types; andwherein the ratio of the first fullerene derivative to the secondfullerene derivative is between about 97:3 and about 60:40.

In some embodiments, the first fullerene derivative is amethanofullerene.

In some embodiments, the first fullerene is a Diels-Alder adduct.

In some embodiments, the second fullerene derivative is a Diels-Alderadduct.

In some embodiments, the second fullerene derivative is amethanofullerene.

In some embodiments, the first fullerene derivative is a Diels-Alderadduct and the second fullerene derivative is a methanofullerene.

In some embodiments, the first fullerene derivative is amethanofullerene and the second fullerene derivative is a Diels-Alderadduct.

In some embodiments, the first fullerene derivative is a C₆₀-basedfullerene derivative and the second fullerene derivative is a C₇₀-basedfullerene derivative.

In some embodiments, the first fullerene derivative is a C₇₀-basedfullerene derivative and the second fullerene derivative is a C₆₀-basedfullerene derivative.

In some embodiments, the first fullerene derivative and the secondfullerene derivative are C₆₀-based fullerene derivatives.

In some embodiments, the first fullerene derivative and the secondfullerene derivative are C₇₀-based fullerene derivatives.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is between about 97:3 and about 70:30.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is between about 95:5 and about 70:30.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is between about 92:8 and about 70:30.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is between about 97:3 and about 75:25.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is about 95:5.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is about 90:10.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is about 85:15.

In some embodiments, the ratio of the first fullerene derivative and thesecond fullerene derivative is about 75:25.

In some embodiments, the composition further comprises a third fullerenederivative.

In some embodiments, the composition further comprises a non-fullerenematerial serving as electron acceptor.

In some embodiments, the non-fullerene material comprises a quantum dot.

In some embodiments, the non-fullerene material emits photons afterlight absorption. The emitted photons may be absorbed in the activelayer, e.g., by the donor material, and form excitons thereby generatingadditional charge transport.

In some embodiments, the methanofullerene is selected from the groupconsisting of phenyl-C₆₁-butyric-acid-methyl-ester ([60]PCBM),thiophenyl-C₆₁-butyric-acid-methyl-ester ([60]ThCBM), [70]PCBM,phenyl-C₆₁-butyric-acid-hexyl-ester ([60]PCBC₆),phenyl-C₇₁-butyric-acid-hexyl-ester ([70]PCBC₆) and other [6,6]-phenylC₆₁ butyric acid or [6,6]-phenyl C₇₁ butyric acid derivatives.

In some embodiments, the Diels-Alder adduct is selected from the groupconsisting of optionally substituted indene, n-hexyl-esters,α-substituted o-quinodimethane, and esters of 3-(1-indenyl) propionicacid.

In some embodiments, the first fullerene derivative is [60]PCBM or[70]PCBM, and the second fullerene derivative is a Diels-Alderindene-adduct, α-substituted o-quinodimethane-adduct, or ester of3-(1-indenyl) propionic acid.

In some embodiments, the first fullerene derivative is [60]PCBM, and thesecond fullerene derivative is

In some embodiments, the composition further comprises a semiconductingpolymer.

In some embodiments, the semiconducting polymer is selected from thegroup consisting of poly(3-hexylthiophene),(poly[2-(3,7-dimethyloctyloxy)-5-methyloxy]-para-phenylene vinylene)(MDMO-PPV), carbazole-based copolymers, diketopyrrolopyrrole (DPP)-basedcopolymers, cyclopentadithiophene-based copolymers, and small moleculesincluding some liquid crystals (e.g., functionalizedhexabenzoncoronene), pentacene derivatives, oligothiophenes,triphenylamines, functionalized anthradithiophenes and a number oftraditional low molecular weight colorants, e.g., from the thiophene-and indoline series.

In a second aspect of the invention, an organic photovoltaic device isprovided comprising a composition comprising a first fullerenederivative and a second fullerene derivative; wherein the first andsecond fullerene derivative are of different types; and wherein theratio of the first fullerene derivative to the second fullerenederivative is between about 97:3 and about 60:40.

In some embodiments, the device has increased stability relative to OPVdevices that are not comprised of two fullerene derivatives. In someembodiments, the device has increased stability relative to OPV devicesthat are not comprised of two fullerene derivatives of different types.

In some embodiments, the device has increased thermal stability whenheated under air to 120° C. relative to OPV devices that are notcomprised of two fullerene derivatives.

In some embodiments, the device has increased stability when submittedto irradiation of 1 sun intensity relative OPV devices that are notcomprised of two fullerene derivatives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary schematic of device architecture of devices usingPV2001 as donor material and [60]PCBM, Blend I or Blend II as acceptormaterial in the active layer.

FIG. 2 is an exemplary schematic of device architecture of devices usingPCE-11 as donor material and [60]PCBM, Blend I, or Blend II as acceptormaterial in the active layer.

FIG. 3A is a graph of the power conversion efficiency (PCE, %) ofITO/ZnO/PV2001:acceptor/PEDOT:PSS/silver nanowire (AgNW) devices as afunction of annealing time (in air at 120° C.) using [60]PCBM, Blend I,or Blend II as acceptor material.

FIG. 3B is a graph of the fill factor (FF, %) ofITO/ZnO/PV2001:acceptor/PEDOT:PSS/silver nanowire (AgNW) devices as afunction of annealing time (in air at 120° C.) using [60]PCBM, Blend I,or Blend II as acceptor material.

FIG. 3C is a graph of the short circuit current (J_(sc), mA/cm²) ofITO/ZnO/PV2001:acceptor/PEDOT:PSS/silver nanowire (AgNW) devices as afunction of annealing time (in air at 120° C.) using [60]PCBM, Blend I,or Blend II as acceptor material.

FIG. 3D is a graph of the open circuit voltage (V_(oc), V) ofITO/ZnO/PV2001:acceptor/PEDOT:PSS/silver nanowire (AgNW) devices as afunction of annealing time (in air at 120° C.) using [60]PCBM, Blend I,or Blend II as acceptor material.

FIG. 3E is a graph of the light injection at 1.2 V (mA/cm²) ofITO/ZnO/PV2001:acceptor/PEDOT:PSS/silver nanowire (AgNW) devices as afunction of annealing time (in air at 120° C.) using [60]PCBM, Blend I,or Blend II as acceptor material.

FIG. 4A is a graph of the power conversion efficiency (PCE, %) ofITO/ZnO/PCE-11:acceptor/evaporated MoO_(x)/evaporated silver (Ag)devices as a function of annealing time (in air at 120° C.) using[60]PCBM, Blend I, or Blend II as acceptor material.

FIG. 4B is a graph of the fill factor (FF, %) ofITO/ZnO/PCE-11:acceptor/evaporated MoO_(x)/evaporated silver (Ag)devices as a function of annealing time (in air at 120° C.) using[60]PCBM, Blend I, or Blend II as acceptor material.

FIG. 4C is a graph of the short circuit current (J_(sc), mA/cm²) ofITO/ZnO/PCE-11:acceptor/evaporated MoO_(x)/evaporated silver (Ag)devices as a function of annealing time (in air at 120° C.) using[60]PCBM, Blend I, or Blend II as acceptor material.

FIG. 4D is a graph of the open circuit voltage (V_(oc), V) ofITO/ZnO/PCE-11:acceptor/evaporated MoO_(x)/evaporated silver (Ag)devices as a function of annealing time (in air at 120° C.) using[60]PCBM, Blend I, or Blend II as acceptor material.

FIG. 4E is a graph of the light injection at 1.2 V (mA/cm²) ofITO/ZnO/PCE-11:acceptor/evaporated MoO_(x)/evaporated silver (Ag)devices as a function of annealing time (in air at 120° C.) using[60]PCBM, Blend I, or Blend II as acceptor material.

FIG. 5 is a graph of the Normalized Power Conversion Efficiency (PCE)over time of PCE-11 with the three acceptor materials [60]PCBM, Blend Iand Blend II under constant illumination with 1 sun LED light at 65° C.and under short circuit condition.

DETAILED DESCRIPTION

The initial PCE of devices using low-band-gap polymers as electron-donormaterials has increased; however, stability, as assessed, e.g., by lightsoaking experiments, was often disappointing. Strategies to eliminate orat least minimize the decrease of the PCE over time (which is usuallydriven by a decrease of the short circuit current, J_(sc)) include theuse of C₇₀ derivatives as electron acceptor material. However, the useof C₇₀-derivative at an industrial level, is, at least at the currentstage, economically not viable, taking into account the approximately10-fold higher price of C₇₀-derivatives in comparison to C₆₀derivatives. In addition, some blends of electron acceptor materialshave been reported to reduce performance significantly due to thepresence of electron traps (Lenes et al., Adv. Funct. Mater. 2009, 19,3002-3007; Cowan et al., Adv. Funct. Mater. 2011, 21, 3083-3092; eachherein incorporated by reference in its entirety). Differences infunctionalization of blended acceptors can lead to different electronicstructures, particularly LUMO levels, creating electronic traps andlowering overall performance. Differences in functionalization can leadto undesirable morphology which may decrease the stability of a device.Differences in functionalization may leave an undesirable morphologyunimproved so that a disappointing stability of a device is maintained.Well-performing devices with increased stability using blends areunexpected.

Organic photovoltaic devices, methods of making and uses thereof aredescribed herein. The devices comprise fullerene derivatives aselectron-acceptor materials.

In one aspect of the invention blends of electron-acceptor materials areused in devices based on a bulk heterojunction (BHJ) in which at leasttwo electron acceptors are fullerene derivatives of different types,i.e., not bearing the same adduct groups. Using such blends in asuitable ratio of the two components does not only lead to a similarinitial PCE as a BHJ with the same low band gap electron donor polymerand a pure [60]PCBM or [70]PCBM as electron acceptor material. Thisblend also allows for significantly increased stability under lightsoaking conditions, which is desirable for organic photovoltaic (OPV)devices.

In the past, compositions of pure fullerenes or fullerene derivativeswere preferred for OPV applications. C₆₀ and C₇₀ fullerenes havedifferent electronic structures, including different LUMO levels (Yanget al., J. Am. Chem. Soc. 1995, 117, 7801-7804; herein incorporated byreference in its entirety). Similarly, fullerene derivatives ofdifferent types have different electronic structures. Fullerene blendswere undesirable because these different electronic structures lead toenergy traps that trap electrons and contribute to recombination ofelectron hole pairs. Recombination of electron hole pairs limits theshort-circuit current. Additionally, blends of fullerene derivativesincrease disorder of polymer-acceptor blends, which may additionallydecrease electron mobility and energy conversion efficiency.Surprisingly, blends with suitable ratios of fullerene derivatives ofdifferent types can have an initial PCE similar to or greater thancompositions of pure fullerenes while also having increased stability.

Fullerene Derivatives

Fullerene derivatives include, e.g., methanofullerenes, Prato fullerenederivatives, Bingel fullerene derivatives, diazoline fullerenederivatives, azafulleroid, ketolactams, and Diels-Alder fullerenederivatives. Fullerene derivatives can bear one or more functionalgroups. In the case of multiple functionalization (usually 2 or 3), thefunctional groups can be identical or different. Fullerene derivativesare disclosed, for example, in International Patent Publication WO2015/192942, U.S. Patent Publication No. 2013/0306944, U.S. PatentPublication No. 2017/0294585, U.S. Pat. Nos. 8,435,713, and 9,527,797(each herein incorporated by reference in its entirety). Other fullerenederivatives include endohedral fullerene derivatives and open cagefullerenes. Examples are described (but not limited to those) in Ross etal. (Nature Materials 2009, 8, 208-212, endohedrals) and Chen et al.(Adv. Energy Mater. 2011, 1, 776-780, open cage fullerenes), each hereinincorporated by reference in its entirety.

Methanofullerenes have the general form

where A is a fullerene; X and Y are independently aryl, alkyl or othergroups bonded via diazoalkane addition; and n is an integer between 1and 6. In some embodiments, X and Y are independently aryl or alkyl; andn is an integer between 1 and 4. In some embodiments, X and Y areindependently aryl or alkyl; and n is 1 or 2. In some embodiments, X andY are independently aryl or alkyl; and n is 1. Non-limiting examples ofmethanofullerenes include phenyl-C₆₁-butyric-acid-methyl-ester([60]PCBM), thiophenyl-C₆₁-butyric-acid-methyl-ester ([60]ThCBM),[70]PCBM, phenyl-C₆₁-butyric-acid-hexyl-ester ([60]PCBC₆),phenyl-C₇₁-butyric-acid-hexyl-ester ([70]PCBC₆) and other [6,6]-phenylC₆₁ butyric acid or [6,6]-phenyl C₇₁ butyric acid derivatives (C₆₀-PCBXor C₇₀-PCBX). Methanofullerenes can be prepared, for example, asdescribed in U.S. Pat. No. 8,435,713 and U.S. Patent Publication No.2005/0239717 (each herein incorporated by reference in its entirety).Methanofullerenes are frequently blended with polymers to serve aselectron acceptors in OPV devices. A blend of [60]PCBM and [70]PCBM maybe prepared as described in U.S. Patent Publication No. 2017/0294585(each herein incorporated by reference in its entirety). C₇₀-PCBX may beprepared as described in U.S. Patent Publication No. 2017/0267628(herein incorporated by reference in its entirety).

In some embodiments, the methanofullerene is

In some embodiments, the methanofullerene is

In some embodiments, the methanofullerene is

Prato derivatives have the general form

where A is a fullerene; R₁ is optionally substituted aryl or aralkyl;and R₂, R₃, R₄, and R₅ are independently optionally substituted alkyl,optionally substituted cycloalkyl, optionally substituted heteroalkyl,optionally substituted heterocycloalkyl, optionally substituted alkenyl,or optionally substituted aralkyl. In some embodiments, R₁ is optionallysubstituted aryl or aralkyl; and R₂, R₃, R₄, and R₅ are independentlyoptionally substituted alkyl, optionally substituted cycloalkyl,optionally substituted heteroalkyl, optionally substitutedheterocycloalkyl, or optionally substituted aralkyl. In someembodiments, R₁ is aryl or aralkyl; and R₂, R₃, R₄, and R₅ areindependently alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, oraralkyl. Prato derivatives include 2-Aza-Propano-(C_(n)+2N). Pratofullerene derivatives may be formed of either C₆₀ or C₇₀.

Bingel derivatives, a sub-class of methanofullerenes, have the generalform

where A is a fullerene; X is an electron withdrawing group; Y is ahydrogen, aryl, substituted aryl, alkyl, substituted alkyl; and z is aninteger between 1 and 6. Nonlimiting examples of electron withdrawinggroups include ester, nitrile, nitro, cyano, ketone, dialkylphosphate,substituted pyridine, trialkylsilyl acetylene, or a trisubstituted silylgroup. In some embodiments, z is an integer between 1 and 4. In someembodiments, z is 1 or 2.

Diazoline derivatives have the general form

where A is a fullerene; R₆ and R₇ are independently aryl.

Azafulleroid derivatives have the general form

where A is a fulleroid; R₉ is an alkyl, aryl, substituted aryl, orSO₂—R₈, wherein R₈ is an alkyl, aryl, or substituted aryl.

Diels-Alder derivatives have the general form

where A is a fullerene; R₁₀ and R₁₁ are independently H, alkyl,alkyloxy, —OC(O)R₁₂, aryl, substituted alkyl, substituted aryl,heteroaryl, or substituted heteroaryl; R₁₂ is independently alkyl,alkyloxy, aryl, substituted alkyl, substituted aryl, heteroaryl, orsubstituted heteroaryl; X is O, alkyl, substituted alkyl, aryl,substituted aryl, heteroaryl, or substituted heteroaryl; Y is aryl,substituted aryl, heteroaryl, substituted heteroaryl, vinylene, orsubstituted vinylene; and n is an integer from 1-20. Nonlimitingexamples of Diels-Alder derivatives include indene-adducts,2-methoxyindene-C₆₀, other alkoxy-substituted indene- ando-quinodimethane-C₆₀ and C₇₀ adducts, α-substitutedo-quinodimethane-adducts, esters of 3-(1-indenyl) propionic acid adductsof C₆₀ or C₇₀, bis-indene-, and bis-o-quinodimethane-C₆₀ and C₇₀adducts.

In some embodiments, the Diels-Alder derivative is

or an ester of 3-(1-indenyl) propionic acid.

In some embodiments, the Diels-Alder derivative is

In some embodiments, the Diels-Alder derivative is

In some embodiments, the Diels-Alder derivative is

Fullerene Blends

Blends of at least two fullerene derivatives may include two or more C₆₀derivatives, two or more C₇₀ derivatives or at least one C₆₀ derivativeand at least one C₇₀ derivative.

Blends of at least two fullerene derivatives may include two or moredifferent types of fullerene derivatives. In some embodiments, each typeof fullerene derivative includes a different type of fullerenederivative.

Blends of at least two fullerene derivatives may additionally comprisenon-fullerene acceptor materials. Nonlimiting examples of non-fullereneacceptors include indacenodithiophene core flanked with benzothiadiazoleand rhodanine groups (IDTBR), indenofluorene analogue of IDTBR (IDFBR),(5Z,50Z)-5,50-{(9,9-dioctyl-9H-fluorene-2,7-diyl)bis[2,1,3-benzothiadiazole-7,4-diyl(Z)methylylidene]}bis(3-ethyl-2-thioxo-1,3-thiazolidin-4-one)(FBR),n-octyl indacenodithiophene (O-IDTBR), 2-ethylhexyl indacenodithiophene(EH-IDTBR) or quantum dots (e.g., Liu et al., Adv. Mater. 2013, 25,5772-5778; Holliday et al., Nature Communications vol. 7, Articlenumber: 11585 (2016); Baran et al., Nature Materials, 2017, 16, 363-369;each herein incorporated by reference in its entirety.)

Blends of two fullerene derivatives may have ratios of about 97:3, 95:5,90:10, 85:15, 80:20, 75:25, 70:30, 60:40 or any ratio in between.

Blends of fullerene derivatives may be formed by adding each fullerenederivative in powder form into solution using, e.g., toluene, o-xylene,o-dichlorobenzene, blends of solvents and additives such as but notlimited to 1,8-octanedithiol.

The blend may then be deposited from solution. The solution may be addedto an antisolvent to aid in precipitation of the blend. The precipitatedblend may be filtered and dried in an oven or vacuum, or a combinationof oven and vacuum. Other methods will be apparent to those skilled inthe art.

In some embodiments, the blend comprises a methanofullerene and aDiels-Alder derivative. The methanofullerene may be C₆₀- or C₇₀-based.In some embodiments, the methanofullerene may be PCBM. The Diels-Alderderivative may comprise an indene adduct substituted at the α-position.

In some embodiments, the blend comprises between about a 97:3 and 60:40ratio of methanofullerene:Diels-Alder derivative. In some embodiments,the blend comprises between about a 97:3 and 60:40 ratio ofDiels-Alder:methanofullerene derivative. In some embodiments, the blendcomprises about a 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, or 60:40ratio of methanofullerene:Diels-Alder derivative. In some embodiments,the blend comprises about a 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, or60:40 ratio of Diels-Alder:methanofullerene derivative. In someembodiments, the blend comprises about a 90:10, or 85:15 ratio ofmethanofullerene:Diels-Alder derivative. In some embodiments, the blendcomprises about a 90:10, or 85:15 ratio of Diels-Alder:methanofullerenederivative.

In some embodiments, the blend comprises [60]PCBM and a C₆₀-indeneadduct (including indene-adducts bearing functional groups at the α- orother positions). In some embodiments, the blend comprises about 95%[60]PCBM and about 5% C₆₀-indene adduct. In some embodiments, the blendcomprises about 90% [60]PCBM and about 10% C₆₀-indene adduct. In someembodiments, the blend comprises about 85% [60]PCBM and about 15%C₆₀-indene adduct. In some embodiments, the blend comprises about 5%[60]PCBM and about 95% C₆₀-indene adduct. In some embodiments, the blendcomprises about 10% [60]PCBM and about 90% C₆₀-indene adduct. In someembodiments, blend comprises about 15% [60]PCBM and about 85% C₆₀-indeneadduct.

In some embodiments, the blend comprises [60]PCBM and a C₇₀-indeneadduct (including indene-adducts bearing functional groups at the α- orother positions). In some embodiments, the blend comprises about 95%[60]PCBM and about 5% C₇₀-indene adduct. In some embodiments, the blendcomprises about 90% [60]PCBM and about 10% C₇₀-indene adduct. In someembodiments, the blend comprises about 85% [60]PCBM and about 15%C₇₀-indene adduct. In some embodiments, the blend comprises about 5%[60]PCBM and about 95% C₇₀-indene adduct. In some embodiments, the blendcomprises about 10% [60]PCBM and about 90% C₇₀-indene adduct. In someembodiments, the blend comprises about 15% [60]PCBM and about 85%C₇₀-indene adduct.

In some embodiments, the blend comprises about 90% [60]PCBM and about10%

In some embodiments, the blend comprises about 10% [60]PCBM and about90%

In some embodiments, the blend comprises about 15% [60]PCBM and about85%

In some embodiments, the blend comprises about 85% [60]PCBM and about15%

In some embodiments, the blend comprises about 90% [60]PCBM and about10%

In some embodiments, the blend comprises about 10% [60]PCBM and about90%

In some embodiments, the blend comprises about 15% [60]PCBM and about85%

In some embodiments, the blend comprises about 85% [60]PCBM and about15%

Measuring Performance

Blends of two or more fullerene derivatives with suitable ratios mayobtain power conversion efficiencies similar or beyond that of currentstate of the art OPV devices. Power conversion efficiency is a measureof the efficiency with which a device converts photons to electricity.

The stability of the device is determined by irradiating the device andmeasuring performance over time under light soaking conditions.Performance may be quantified based on PCE. The stability may bemeasured under various conditions, including temperature, humidity, andlight intensity, depending on the conditions in which the device willoperate. Stability may be determined either be measuring performancecontinuously or by measuring performance before and after a period ofuse.

Organic Photovoltaic Devices

Allowing for the use of inexpensive, high-speed, large-scaleroll-to-roll manufacturing processes, organic photovoltaic devices(OPVs) have a significant chance of becoming important technology forelectricity generation.

OPV devices, also called polymer-solar cells (PSC) or polymer-fullerenecomposite solar cells, are lightweight and can be flexible, opening thepossibility for a range of new applications including large-area pliabledevices.

Without wishing to be bound by theory, in addition to tuning the opticaland electronic properties of the materials used for light harvesting,carrier generation, transport, and collection, control of the nanoscalemorphology of the active layer is another important factor on the pathto increasing power conversion efficiencies (PCE) in the laboratory and,particularly, of large-area devices. Particularly, nanoscale morphologymay be an important factor in the optimization of OPV.

Bulk heterojunction OPVs are a particular class of OPV device, where ananoscale morphology between an electron donor material (in most but notall cases a polymer) and electron accepting material is formed. OPVdevices include in their active layer an electron donor (e.g.,poly(3-hexylthiophene) (P3HT)) blended with electron acceptors, such asfullerenes or their derivatives. When blends of fullerene derivativesare combined with electron donor polymers, the morphology of thefullerene-polymer blend depends on the derivatives and ratio of thefullerene derivative blend. Also, the use of blends of electron-donormaterials have been reported (e.g., Lin et al., Synthetic Metals 2014,192, 113-118; herein incorporated by reference in its entirety.)

The devices can be made, e.g., via liquid deposition of different layerssuch as the electrode, electron transport layer, etc. The active layercomprises an electron acceptor and an electron donor.

Additional suitable electron donor materials include semiconductingpolymers, such as poly(3-hexylthiophene),(poly[2-(3,7-dimethyloctyloxy)-5-methyloxy]-para-phenylene vinylene)(MDMO-PPV), carbazole-based copolymers, cyclopentadithiophene-basedcopolymers, diketopyrrolopyrrole (DPP)-based copolymers and smallmolecules including some liquid crystals (e.g., functionalizedhexabenzoncoronene), pentacene derivatives, oligothiophenes,triphenylamines, functionalized anthradithiophenes and a number oftraditional low molecular weight colorants, e.g., from the thiophene-and indoline series.

General Procedures for Preparation of Fullerenes

Into a vessel is added fullerene derivatives and, optionally, othercompounds in specific proportions to make the desired blend. A solventis added of type and volume suitable to dissolve the component materialsof the blend, preferably completely. In some embodiments, optionally andwithout limitation, solubility can be aided by any combination of time,heat, sonication, stirring, rotation, agitation and/or use of excesssolvent. In some embodiments, once the material is dissolved, preferablycompletely dissolved, some solvent may be optionally removed to achievea desired concentration. In some embodiments, the solvated blend is thenprecipitated by some means, including but not limited to, furtherconcentration and/or the addition of, or addition to an antisolvent. Insome embodiments, it is desirable for the precipitation to be completeand uniform such that the ratio of component materials is about uniformand consistent throughout the product. In some embodiments, theprecipitated material is then filtered, rinsed with the antisolvent andallowed to dry in any number, order or combination of steps using somecombination of vacuum, heat and/or time. In some embodiments, techniquesincluding, but not limited to, sieving may be used to achieve a desiredappearance and/or consistency of the product. The dryness of thematerial can be confirmed by thermogravimetric analysis (TGA). The yieldcan be confirmed by mass once the material is dry. The ratio ofcomponents, purity, and level of consistency throughout the solid can beconfirmed by various methods of characterization including highperformance liquid chromatography (HPLC) analysis.

EXAMPLES

Certain embodiments will now be described in the following non-limitingexamples.

Preparation of Blend I

Blend I was prepared using

[60]PCBM mass equal to nine tenths of the total desired mass of theblend, and Diels-Alder adduct mass equal to one tenth of the totaldesired mass of the blend were added to a rotovap flask large enough toachieve 18 g/L total fullerenes in solvent. The flask was secured to therotovap. O-xylene was added via injection line and negative pressure toachieve 18 g/L of solids in solvent. The contents were stirred at ˜200torr in a 50° C. water bath for 30-60 minutes until solids arecompletely dissolved. The pressure was reduced to evaporate o-xyleneuntil the concentration was 100 g/L. It is preferred not to exceed 100g/L. The fullerene solution in o-xylene was slowly poured into methanolto precipitate the fullerene adducts completely. The mixture was vacuumfiltered through a 393 Sartorius grade filter paper (1-2 micron). Thesolids were rinsed with methanol to push all o-xylene through to thefiltrate. The filtered solids were dried under vacuum, preferably for 12or more hours at 70° C. The solids were removed from the oven,preferably at not more than 50° C., the solids were sieved, and theblend continued to dry for another or more hours at 50° C. and highvacuum. The solids were removed from the oven. The yield of solidsobtained was quantitative. The purity and component ratio based on HPLCanalysis were recorded and the solid was analyzed by TGA to determinethe residual solvent content.

Preparation of Blend II

Blend II was prepared using

[60]PCBM mass equal to nine tenths of the total desired mass of theblend, and Diels-Alder adduct mass equal to one tenth of the totaldesired mass of the blend were added to a rotovap flask large enough toachieve 18 g/L total fullerenes in solvent. The flask was secured to therotovap. O-xylene was added via injection line and negative pressure toachieve 18 g/L of solids in solvent. The contents were stirred at ˜200torr in a 50° C. water bath for 30-60 minutes until solids arecompletely dissolved. The pressure was reduced to evaporate o-xyleneuntil the concentration is 100 g/L. It is preferable not exceed 100 g/L.The fullerene solution in o-xylene was slowly poured into methanol toprecipitate the fullerene adducts completely. The mixture was vacuumfiltered through a 393 Sartorius grade filter paper (1-2 micron). Thesolids were rinsed with methanol to push all o-xylene through to thefiltrate. The filtered solids were dried under vacuum, preferably for 12or more hours at 70° C. The solids were removed from the oven,preferably at not more than 50° C., the solids were sieved, and theblend continued for another 12 or more hours at 50° C. and high vacuum.The solids were removed from the oven from the oven. The yield of solidsobtained was quantitative. The purity and component ratio based on HPLCanalysis was recorded and the solid was analyzed by TGA to determine theresidual solvent content.

Preparation of Devices Using Blend I or Blend II with the Donor PV2001in the Active Layer

Devices with PV2001 as the donor material and Blend I, Blend II, or[60]PCBM as the acceptor material were prepared using an invertedarchitecture as shown in FIG. 1 . Glass substrates (101) (25 mm×25 mm,Standard-Layout, 0.1 cm², resulting in six solar cells on eachsubstrate), precoated with indium tin oxide (ITO) (102), were precleanedby wiping with soft tissue and toluene. Subsequently, the glasssubstrates were further cleaned in an ultrasonic bath, first withacetone and then with IPA, for 5 min, respectively. A ZnO solution inIPA was deposited by doctor blading followed by 4 min annealing at 120°C. under air to form a ZnO oxide layer (103). The active layer (104)included PV2001 as a donor and [60]PCBM, Blend I, or Blend II as theacceptor. In preparation of the active layer ink, 13.5 mg of PV2001(purchased from Raynergy Tek, Hsinchu, Taiwan) and 19.5 mg of [60]PCBM,Blend I or Blend II were dissolved, at a temperature of 120° C. andunder stirring for at least 8 h under nitrogen, in 1 mL of o-xylene,resulting in an optical density of 0.7 to 0.8 measured at 670-675 nm byspectrophotometer, before deposition, by doctor blading, on the top ofthe ZnO oxide layer (103) under ambient conditions. Subsequentlypoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS, HTL388) (105) was deposited as hole transport layer, again by doctorblading, followed by annealing for 4 min at 140° C. in a glove box.Finally, silver nanowires (106) were deposited as top electrode out ofan aqueous solution.

Preparation of Devices Using Blend I or Blend II with the Donor PCE-11in the Active Layer

Devices with PCE-11 as the donor material and Blend I, Blend II, or[60]PCBM as the acceptor material were prepared using an invertedarchitecture as shown in FIG. 2 . Glass substrates (201) (25 mm×25 mm,Standard-Layout, 0.1 cm², resulting in six solar cells on eachsubstrate), precoated with indium tin oxide (ITO) (202), were precleanedby wiping with soft tissue and toluene. Subsequently, the glasssubstrates were further cleaned in an ultrasonic bath, first withacetone and then with IPA, for 5 min, respectively. A ZnO solution wasdeposited by doctor blading followed by 4 min annealing at 120° C. underair to form a ZnO oxide layer. The active layer (207) includes PCE-11 asa donor and [60]PCBM, Blend I, or Blend II as the acceptor. Inpreparation of the active layer ink, 13.5 mg of PCE-11 (PffBT4T-20D,purchased from 1-Material Inc, Dorval, Quebec, Canada) and 19.5 mg of[60]PCBM, Blend I or Blend II were dissolved, at a temperature of 120°C. and under stirring for at least 8 h under nitrogen, in 1 mL ofo-xylene, resulting in an optical density of 0.7 to 0.8 measured at 687nm by spectrophotometer, before deposition, by doctor blading, on thetop of the ZnO oxide layer (203) under ambient conditions. Subsequently,10 nm of MoO_(x) (208) was deposited by evaporation as hole transportlayer. Finally, 100 nm of silver (209) was deposited as top electrode byevaporation.

Stability Measurement

The thermal stability of the devices with both PV 2001 or PCE-11 in theactive layer was assessed by thermooxidation at 120° C. in ambient air,without light. For this purpose, the finalized cells have been measuredin nitrogen at 1 sun. Subsequently, cells have been annealed in air at120° C. in a dark atmosphere. The performance of the cells was measuredregularly as a function of the annealing time. For this purpose, a solarsimulator (LOT Quantum Design LSO916) and a source measurement unitKEYSIGHT B2901A were used. After each measurement the cells were putback in the oven to continue the annealing procedure. A potential from−1 to 1.5 V was applied to the device while the device was irradiatedand the current measured. The power conversion efficiency, fill factor,short circuit current, open circuit voltage, and light injection datawere extracted from the resulting current-voltage (I-V) curve. Powerconversion efficiency (PCE, %), fill factor (FF, %), short circuitcurrent (J_(sc), mA/cm²), open circuit voltage (V_(oc), V), and lightinjection at 1.2 V (mA/cm²) of the devices using PV2001 as donormaterial are shown in FIGS. 3A-3E, while the corresponding data from thedevices using PCE-11 as donor material are given in FIGS. 4A-4E.

An increased thermal stability of Blends I and II, in comparison to theuse of [60]PCBM, has been observed for both investigated donormaterials, PV 2001 and PCE-11. The decrease of performance over timeobserved for all materials systems investigated here, but significantlyless pronounced using Blend I or Blend II, has been mainly driven by thedecrease of the short circuit current (J), shown in FIG. 3C and FIG. 4C.Such improved thermal stability is of significant commercial relevance,particularly in application where an annealing process step of limitedduration, for instance, in the context of device integration isrequired.

Furthermore, lifetime measurements were conducted under LED-lightexposure approximating solar light (without UV) at an intensity of 1 sununder inert gas and a controlled temperature of 65° C. The evolution ofthe power conversion efficiency (PCE), normalized to initialmeasurements, for [60[PCBM, Blend I and Blend II, using PCE-11 as donormaterial, is shown in FIG. 5 over a duration of 650 h. Both Blend I andBlend II showed evidence of enhanced long-term stability in comparisonto [60]PCBM as acceptor material. The continuation of the light-exposureis expected to show even more accentuated differences.

As will be apparent to one of ordinary skill in the art from a readingof this disclosure, further embodiments of the present invention can bepresented in forms other than those specifically disclosed above. Theparticular embodiments described above are, therefore, to be consideredas illustrative and not restrictive. Those skilled in the art willrecognize, or be able to ascertain, using no more than routineexperimentation, numerous equivalents to the specific embodimentsdescribed herein. Although the invention has been described andillustrated in the foregoing illustrative embodiments, it is understoodthat the present disclosure has been made only by way of example, andthat numerous changes in the details of implementation of the inventioncan be made without departing from the spirit and scope of theinvention, which is limited only by the claims that follow. Features ofthe disclosed embodiments can be combined and rearranged in various wayswithin the scope and spirit of the invention. The scope of the inventionis as set forth in the appended claims and equivalents thereof, ratherthan being limited to the examples contained in the foregoingdescription.

What is claimed is:
 1. A composition comprising a first fullerenederivative comprising a methanofullerene; and a second fullerenederivative comprising a Diels-Alder adduct comprising a substitutedindene; wherein the ratio of the first fullerene derivative to thesecond fullerene derivative is between about 97:3 and about 70:30. 2.The composition of claim 1, wherein the first fullerene derivative is aC₆₀-based fullerene derivative and the second fullerene derivative is aC₇₀-based fullerene derivative.
 3. The composition of claim 1, whereinthe first fullerene derivative is a C₇₀-based fullerene derivative andthe second fullerene derivative is a C₆₀-based fullerene derivative. 4.The composition of claim 1, wherein the first fullerene derivative andthe second fullerene derivative are C₆₀-based fullerene derivatives. 5.The composition of claim 4, wherein the first fullerene derivative andthe second fullerene derivative are C₇₀-based fullerene derivatives. 6.The composition of claim 1, wherein the ratio of the first fullerenederivative and the second fullerene derivative is between about 95:5 andabout 70:30.
 7. The composition of claim 1, wherein the ratio of thefirst fullerene derivative and the second fullerene derivative isbetween about 92:8 and about 70:30.
 8. The composition of claim 1,wherein the ratio of the first fullerene derivative and the secondfullerene derivative is about 95:5.
 9. The composition of claim 1,wherein the ratio of the first fullerene derivative and the secondfullerene derivative is about 90:10.
 10. The composition of claim 1,further comprising a third fullerene derivative.
 11. The composition ofclaim 1, further comprising a non-fullerene acceptor.
 12. Thecomposition of claim 1, further comprising a quantum dot.
 13. Thecomposition of claim 1, wherein the first fullerene derivative comprisesa methanofullerene selected from the group consisting ofphenyl-C₆₁-butyric-acid-methyl-ester ([60]PCBM),thiophenyl-C₆₁-butyric-acid-methyl-ester ([60]ThCBM), [70]PCBM,phenyl-C₆₁-butyric-acid-hexyl-ester ([60]PCBC₆),phenyl-C₇₁-butyric-acid-hexyl-ester ([70]PCBC₆) and other [6,6]-phenylC₆₁ butyric acid or [6,6]-phenyl C₇₁ butyric acid derivatives.
 14. Thecomposition of claim 1, wherein the second fullerene derivativecomprises an ester of 3-(1-indenyl) propionic acid.
 15. The compositionof claim 1, wherein the first fullerene derivative is [60]PCBM or[70]PCBM, and the second fullerene derivative is an ester of3-(1-indenyl) propionic acid.
 16. The composition of claim 1, whereinthe first fullerene derivative is [60]PCBM, and the second fullerenederivative is


17. The composition of claim 1, further comprising a semiconductingpolymer.
 18. An OPV device comprising the composition of claim 1,wherein the device has increased thermal stability relative to OPVdevices that are not comprised of two fullerene derivatives.
 19. An OPVdevice comprising the composition of claim 1, wherein the device hasincreased thermal stability when heated under air to 120° C. relative toOPV devices that are not comprised of two fullerene derivatives.
 20. AnOPV device comprising the composition of claim 1, wherein the device hasincreased stability when submitted to irradiation of 1 sun intensityrelative OPV devices that are not comprised of two fullerenederivatives.
 21. The composition of claim 1, wherein the first fullerenederivative is [60]PCBM, and the second fullerene derivative is


22. A composition comprising a first fullerene derivative comprising aDiels-Alder adduct; and a second fullerene derivative comprising amethanofullerene; wherein the ratio of the first fullerene derivative tothe second fullerene derivative is between about 97:3 and about 70:30.23. The composition of claim 22, wherein the Diels-Alder adductcomprises a substituted indene.
 24. The composition of claim 22, whereinthe first fullerene derivative is a C₆₀-based fullerene derivative andthe second fullerene derivative is a C₇₀-based fullerene derivative. 25.The composition of claim 22, wherein the first fullerene derivative is aC₇₀-based fullerene derivative and the second fullerene derivative is aC₆₀-based fullerene derivative.
 26. The composition of claim 22, whereinthe first fullerene derivative and the second fullerene derivative areC₆₀-based fullerene derivatives.
 27. The composition of claim 22,wherein the first fullerene derivative and the second fullerenederivative are C₇₀-based fullerene derivatives.
 28. The composition ofclaim 22, wherein the ratio of the first fullerene derivative and thesecond fullerene derivative is between about 95:5 and about 70:30. 29.The composition of claim 22, wherein the ratio of the first fullerenederivative and the second fullerene derivative is between about 92:8 andabout 70:30.
 30. The composition of claim 22, wherein the ratio of thefirst fullerene derivative and the second fullerene derivative is about95:5.
 31. The composition of claim 22, wherein the ratio of the firstfullerene derivative and the second fullerene derivative is about 90:10.32. The composition of claim 22, further comprising a third fullerenederivative.
 33. The composition of claim 22, further comprising anon-fullerene acceptor.
 34. The composition of claim 22, furthercomprising a quantum dot.
 35. The composition of claim 22, wherein thesecond fullerene derivative comprises a methanofullerene selected fromthe group consisting of phenyl-C₆₁-butyric-acid-methyl-ester ([60]PCBM),thiophenyl-C₆₁-butyric-acid-methyl-ester ([60]ThCBM), [70]PCBM,phenyl-C₆₁-butyric-acid-hexyl-ester ([60]PCBC₆), and other [6,6]-phenylC₆₁ butyric acid.
 36. The composition of claim 22, wherein the firstfullerene derivative comprises a Diels-Alder adduct selected from thegroup consisting of optionally substituted indene, α-substitutedo-quinodimethane, optionally substituted o-quinodimethane, and an esterof 3-(1-indenyl) propionic acid.
 37. The composition of claim 22,wherein the first fullerene derivative is an optionally substitutedDiels-Alder indene-adduct, α-substituted o-quinodimethane-adduct,optionally substituted o-quinodimethane adduct, or ester of3-(1-indenyl) propionic acid adduct, and the second fullerene derivativeis [60]PCBM.
 38. The composition of claim 22, wherein the firstfullerene derivative is

and the second fullerene derivative is [60]PCBM.
 39. The composition ofclaim 22, further comprising a semiconducting polymer.
 40. An OPV devicecomprising the composition of claim 22, wherein the device has increasedthermal stability relative to OPV devices that are not comprised of twofullerene derivatives.
 41. An OPV device comprising the composition ofclaim 22, wherein the device has increased thermal stability when heatedunder air to 120° C. relative to OPV devices that are not comprised oftwo fullerene derivatives.
 42. An OPV device comprising the compositionof claim 22, wherein the device has increased stability when submittedto irradiation of 1 sun intensity relative OPV devices that are notcomprised of two fullerene derivatives.
 43. The composition of claim 22,wherein the second fullerene derivative comprises a methanofullereneselected from the group consisting of [70]PCBM,phenyl-C₇₁-butyric-acid-hexyl-ester ([70]PCBC₆), and other [6,6]-phenylC₇₁ butyric acid derivatives.
 44. The composition of claim 22, whereinthe first fullerene derivative is an optionally substituted Diels-Alderindene-adduct, α-substituted o-quinodimethane-adduct, optionallysubstituted o-quinodimethane adduct, or ester of 3-(1-indenyl) propionicacid adduct, and the second fullerene derivative is [70]PCBM.
 45. Thecomposition of claim 22, wherein the first fullerene derivative is

and the second fullerene derivative is [60]PCBM.